The present invention relates generally to the field of disc drive data storage devices and more particularly, but without limitation, to the efficient switching among read/write heads of a disc drive to reduce damage to elements of the heads.
Hard disc drives are used in modern computer systems and computer networks to enable users to quickly access vast amounts of electronically stored data. A typical disc drive houses five to ten magnetic discs which are axially aligned and mounted to a spindle motor for rotation at a constant, high speed. An array of read/write heads are controllably positioned adjacent magnetic recording surfaces of the discs in order to store and retrieve the data from tracks defined on the disc surfaces. The heads fly adjacent the recording surfaces on air bearings established by air currents set up by the rotation of the discs.
Of particular interest are heads of the so-called xe2x80x9cmagneto-resistivexe2x80x9d variety, which utilize magneto-resistive (MR) elements to sense the selective magnetization of the tracks during disc drive data transfer operations. A typical MR element is formed from an alloy of materials so as to have a baseline electrical resistance which varies in the presence of a magnetic field of a selected orientation. By passing a bias current through the MR element, the selective magnetization of a corresponding track can be determined in relation to variations in voltage detected across the MR element.
It is common in present generation disc drive manufacturing processes to individually select read bias current magnitudes for each of the MR heads of a disc drive in order to optimize disc drive performance. For example, test data are typically written and then read in turn a number of times using a range of different read bias current magnitudes. Those read bias current magnitudes providing optimum performance are then stored in memory utilized by the drive so that, when a particular head is selected during subsequent operation, the disc drive applies the appropriate read bias current to the particular head.
MR heads are known to be delicate and must be handled and operated it with a certain degree of care so as to prevent inadvertent damage which can degrade the reliability of the heads. Although the application of a relatively larger bias current will generally enhance the sensitivity of an MR head during a read operation, by providing a higher signal to noise ratio in a recovered readback signal, it is important to ensure that the maximum power dissipation capability of the head is not exceeded. As will be recognized, because the MR element operates as a (highly sensitive) resistance, the power P dissipated by the MR element will be generally proportional to the resistance R of the MR element multiplied by the square of the bias current I (i.e., P=I2R). Accordingly, there is all upper limit on the magnitude of the bias current that can be applied to any given MR head, and the application of too large a bias current, even momentarily, can stress the MR head and adversely affect its operational reliability over time.
Accordingly, as efforts continue to provide disc drives with ever increasing levels of data storage capabilities and performance, there remains a continual need for improvements in the art whereby the reliability of the drives can be maintained by minimizing inadvertent stresses upon sensitive components of the drives, such as MR heads.
The present invention is directed to an apparatus and method for minimizing damage to a disc drive during head switching operations.
In accordance with a preferred embodiment, the disc drive comprises a plurality of magnetic recording surfaces to and from which data are transferred using read/write heads, each head utilizing the application of a bias current during operation. Preferably, the heads are characterized as magneto-resistive heads, each having a magneto-resistive read element.
To switch from a presently selected head to a target head, the disc drive determines a first value indicative of the magnitude of a bias current for the presently selected head and a target bias current to be applied to the target head. When the second value is greater than the first value, the disc drive switches from the presently selected head to the target head and then applies the target bias current; conversely, when the first value is greater than the second value, the target bias current is applied to the presently selected head and then the disc drive switches from the presently selected head to the target head.
The disc drive preferably comprises a preamplifier circuit which is operably coupled to the heads and applies the bias currents to the heads in response to a read bias value provided by a head selection control circuit, such as a disc drive control processor. The head selection control circuit further preferably causes the preamplifier circuit to individually select the heads in response to a head select value. The head bias and head select values are preferably expressed as part of a multi-bit digital word and are provided to a register of the preamplifer by way of a serial input path.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.